# ASTR1000 University of Colorado Volcanoes on Jovian Moons & Planetary Rings Questions

(1) Volcanoes on Jovian Moons

(6 pts.) In another solar system, we discover two Jovian moons that have very different levels of volcanism. Propose three hypotheses and explain how each of them could account for this difference.

(2) Regular vs. Irregular

(2 pts.) (a) Give 3 properties of a regular satellite, that is, a satellite with a regular orbit:
(1 pt.) (b) Provide an example of a regular satellite:
(1 pt.) (c) Provide an example of an irregular satellite:
(2 pts.) (d) What is inferred about the origin of a satellite from the regularity/irregularity of its orbit?
(3 pts.) (e) Suppose we find a moon orbiting around a planet at a distance of 100,000 km, and a student says: “Perhaps this moon was originally an asteroid orbiting the Sun, and it just happened to drift close to the planet until it as only 100,000 km away from it, where it was caught by the planet’s gravity, and it has been orbiting here ever since.” Using the law of conservation of energy, explain why this scenario is physically impossible, and why a capture process must be more complicated than this. Please ignore the effect of the Sun’s graity in your analysis. It is irrelevant.

(3) Titan

(6 pts.) Astronomers were amazed to discover evidence of rain, rivers, lakes, seas, and river deltas on Saturn’s moon Titan. However, many astrobiologists are still skeptical that we will find living organisms in the lakes and seas of Titan. Write a paragraph discussing this issue and explaining the source of this skepticism.

(4) Making a Model of Planetary Rings

(3 pts.) (a) The rings of Saturn are about 70,000 kilometers across but only 20 meters thick. Suppose you wanted to build a model of Saturn’s rings out of a sheet of plastic that is 1.5 mm thick. To keep the proportions right, how large a sheet of plastic would you need to make the scale model realistic? Show your work.
(3 pts.) (b) To model Uranus’ thin rings, strings of spaghetti (or perhaps, strictly speaking, linguini) would be more appropriate than sheets of plastic. Uranus’ rings are also only about 20 meters thick and extend around the planet in a thin ring at a radius of about 50,000 km. If you wanted to build a model of Uranus’ ring using 3 mm thick pasta – how long a piece of spaghetti would you need? Show your work.

(5) Rings

(4 pts.) In another solar system we discover two jovian planets which are very similar, yet one has an extensive icy ring system, while the other has negligible rings. Propose a hypothesis to explain why this difference might exist.

(6) Distances and Velocities

(3 pts.) (a) A space probe is launched on a mission requiring it to travel a distance of 3.5 AU in 14 months. What must be this space probe’s average speed? Give your answer in kilometers per second.

(3 pts.) (b) A space probe is 16 AU from the Earth. How much time will it take its radio signals to travel through space to reach us? Give your answer in hours.

(3 pts.) (c) If it takes 4.78 hours for light from a comet to reach us, what is its distance? Give your answer in AU.